Arc lamp electrode



Patented June 7, 1932 UNITED STATES PATENT @FFIQE MARGEL OSWALD, OF NANTERRE, FRANCE, ASSIG-NOR TO OOMPAGNIE LORRAINE DE OHARBONS POUR LELECTRICITE, OF PARIS, FRANCE, A CORPORATION OF FRANCE ARC LAMP ELECTRODE No Drawing. Application filed April 16, 1928, Serial No. 270,580, and in France April 21, 1927.

It is known that electric arcs are considerably stabilized by introducing into the flame of the arc an appropriate mineral material containing metals of low ionization potential. Among them, the alkaline metals and alkaline earth metals, certain metals of the iron group, the metals of the rare earths etc., are much the most employed. Particularly the metals of the rare earthsgive a white arc flame, slightly bluish, of which the actinic value is very high. This are is used for this reason for taking pictures in studios and in photogravure.

It has, however, been observed, that these I 16 rare earth arcs do not have perfect stability,

in thatthe inevitable fluctuations of the light produce an irregularity in density of the films. It has been possible to remedy this inconvenience somewhat by associating with 20 the rare earths, small quantities of metals with low ionization potential, like calcium, barium or the alkaline metals, but this remedy is not suflicient and the scenic directors instinctively fear that the yellow or orange colour produced by bodies like sodium or calcium spoils the actinic eflect.

The invention hereinafter described has for its object to remove all these drawbacks without changing the colour of the arc.

According to the present invention, a perfectly stabilized arc is produced, by introducing into the positive carbon or into the two carbons, small quantities (up to about two per cent) of a refractory reducing mate- 35 rial adapted to increase the stability of the arc flame, namely, non-oxidized or slightly oxidized silicon, such as silicon, silicon carbide or silicon oxy-carbide, and the equivalents thereof like boron and zirconium, their non-oxidized or only slightly oxidized compounds, carbides or oxy-carbides.

It has been found that the refractory reducing materials according to the invention are adapted to increase the stability of the are flame due to their chemical properties, and this by effecting the reduction of the oxygenated compounds incorporated in the carbons as mineralizers, in the manner described hereinafter, which compounds otherwise produce the disturbing effect above noted due to their reduction by the carbon in or near the crater of the arc.

The refractory reducing materials according to the invention are incorporated as adjuvants in the already mineralized carbons, which may be mineralized with the rare earths or the alkalies, preferably with compounds of the cerium group. To this end the positive carbon, for example may be cored with a paste containing an organic binding material in solution, or in emulsion in water, and an intimate mixture of silicon, or of one of the compounds mentioned above, with the rare earths of the cerium group, these latter being in the state of oxides, fluorides or oxyfluorides, and also with carbonaceous powders which conveniently dilute the mineral materials. For example, the core hole of this carbon being about one third of the external diameter, the paste will be formed by 50 per cent of carbonaceous materials, 48 to 49 per cent composed of the rare earths, and the remainder by silicon or, preferably, carborundum, which is less expensive and which is more easily obtained in commerce.

After mixing the powders intimately, a thick solution of dextrin, gum arabic or any other organic binding material is added so as to finally obtain an extremely thick paste, which is injected under pressure in the carbon tube, in a known manner.

The negative carbon could be formed with an analogous composition, but it has been found experimentally that it is much better to substitute for the rare earths much smaller quantitiesoof potassium carbonate or borate, these salts being capable of being associated with carborundum exactly as for the positive carbon.

Of course the invention is not limited to the examples given above, and consists, in a more general manner, in the incorporation in an arc lamp carbon, such as in the core of the positive or negative carbon, of silicon, boron or zirconium, or a carbide or oxycarbide of these elements, or compounds of these elements, such as the silicide of boron.

All these materialsare associated in a low proportion with a metallic mineralizing element of low ionization potential,this metallie element, or the mixture of the said elements being selected according to the desired effect to be obtained.

The said carbons can also be made by introducing a previously hardened homogeneously mineralized rod into a tube of carbon, the union between the homogeneous interior and the tube being effected by means of an adhesive according to Well-known methods.

The invention also contemplates the introduction. of adjuvants like-silicon orboron into the shell of carbon, Whilst the mineral materials, like the rare earths, areseparately introduced into the cores. The .results from this method may be favourably compared with those obtained by the method described above. It is nevertheless necessary .to take .into account in this manner of-carryingout the invention, that .the proportion of ,adjuvants may be raised in ICOIlSBqL16IlC8,'b6 causea part is lost by Ilateralcombustion of the carbon before it arrives ,-in the arc.

It should be noted thattheterm refractory reducing materialadapted to increase 'the stability of the arc fiame,.as used in some of .theclaims herein, is intended to describe and refer to the :materials herein described, as producing the improved effects v.noted, namely, silicon, silicon carbide, silicon oxycarbide, and the equivalents ithereof, With particular reference to boron, boroncarbide, zirconium, zirconium carbide, boron silicide, .etc. It should also be noted that the term refractory reducing silicon .material, as usedin some of the claims herein, is intended to cover and include siliconzandrnon-oxidized or slightly oxidized compounds-thereof, with particular reference to silicon carbide and silicon oXy-carbide.

It should also be noted that it is essential herein that the materials referred to above should be of a reducing character, that is, thatno materialsshouldbe usedexcept those which are non-oxygen containing or only slightly oxygen containing, for the following reasons:

(a) The-effect is not equivalent when one incorporates in the arc lamp carbons, as adjuvants, already oxidized substances in the one case or refractory reducing substances in the second case, as said "carbons already contain important quantities of mineralizing materials,generallyinthe form of rare earths, and these latter, even if used in the form of commercial fluorides, are not free from oxy- When the rare earth oxides are subjected 'to the action of the are, .a violent reductionbythecarbon-takesplace and a fusiblecarbide is formed with an-ebullition which detaches incandescent ,particles which are shot ofi parallelly to the varc and cause fluctuations in the light. This disadvantage subsists When-oxidized substances such as silica or boric acid are employed as .adjuv-ants,

(0) On the contrary, when refractory reducing materials like silicon, boron and zirconium, or their carbides, or cry-carbides, are used, the reduction of the oxidized compounds of the rare earths is effected in the mass ofthe carbon, in azone already incandescent but which has not yet :reached the crater. The reduction is much less violent and, as it takes place in the mass of the car- -bon,beloW-thecrater, the arcremain-s perfectlystable.

It should also be noted that it is essential for'the effects noted herein, that the silicon, siliconcarbide or the like, be employed in very low percentages, not greatly exceeding about two percent, since it has been found :by' experimentthat the vapourization of these adjuvants adds :but .feW linesto .the spectrum of the arc'and consequently lowers the luminous output-thereof and, therefore, that the percentage incorporated should be kept as low as possible Whilst obtaining the desired result. Further, the above :limit given has also been found to be necessary in order to avoid too violent a reduction of :the rare earth oxidesnear the-crater of the are.

1. An arc lamp electrode comprising car- :bon, a 'minerali-zing material including an oxygen-containing metallic compound of low ionization potential, and up to about 2 per cent-of airefractory reducing'material adapted to'increase the stability-of the arc flame, intimately mixed :together.

.2. Anarc lamp'electrode comprising carbon, an oxygen-containing rare earth com pound,-andup=to about 2 percent-eta refractory reducing material adapted to increase the stability of the arc flame.

'3. An arc lamp electrode comprising carbon, an oxygen-containing rare earth com- ;pound,-and up to about 2 per cent-of a refractoryrreducing silicon material.

4. An are lamp electrode having a core portion containing'carbon,-a rare earthoxide,

and a refractory reducing material adapted to increase the stability of the-arc :fiame, zin- L-timately :mixed together, said reducing 'ma terial being in an amount up to :about .2 :per cent of the 'total core material.

5. An'arc lamp electrodehaving a core por tion containing carbon, a rare earth oxide,

'anda refractory reducing silicon material in "an amount up to about '2 per cent of the core material, intimately mixed together.

6. An arc llamp electrode having a core portion the diameter of which isabout onethird of the-external diameter of the carbon and containing carbon and rare earth compounds in about equal proportions and from 1 to 2 per cent of a refractory reducing silicon material.

7. An are lamp electrode comprising carbon, an oxygen-containing cerium'conrpound,

and up to about 2 per cent of a refractory reducing silicon material.

8. An arc lamp electrode, for use as a negative electrode, comprising carbon, an oxygen-containing alkali metal compound, and up to about 2 per cent of a refractory reducing material adapted to increase the stability of the arc flame.

9. An arc lamp electrode, for use as a negative electrode, comprising carbon, an oxygen-containing potassium salt, and up to about 2 per cent of a refractory reducing silicon material.

In testimony whereof I have hereunto afixed my signature.

MARGEL OSWALD. 

